Aldehydes and Ketones Lecture Review

Flashcards covering key definitions and concepts related to aldehydes and ketones, their properties, naming conventions, reactions (oxidation, reduction, addition of alcohols), and common examples from Chapter 15 of 'Fundamentals of General, Organic, and Biological Chemistry'.

Carbonyl group

A functional group that has a carbon atom joined to an oxygen atom by a double bond.

Carbonyl molecule

Any molecule that contains a carbonyl functional group (C=O), classified according to what atoms are bonded to the carbonyl carbon.

Polarity of Carbonyl Group

Strong polarization due to oxygen being more electronegative than carbon, responsible for physiochemical properties and reactivity, with bond angles of 120º.

Aldehyde

A compound that has a carbonyl carbon bonded to one carbon and one hydrogen.

Ketone

A compound that has a carbonyl group bonded to two carbons.

IUPAC naming for Aldehydes

Replaces the final -e of an alkane with -al; the carbon chain is numbered starting with the carbonyl carbon.

IUPAC naming for Ketones

Replaces the final -e of the alkane name with -one; the numbering of the alkane chain begins nearest the carbonyl group.

Polarity of Aldehydes and Ketones

Moderately polar due to the polarity of the carbonyl group (δ+ on carbon, δ- on oxygen).

Boiling Points of Aldehydes and Ketones vs. Alkanes/Alcohols

Boil at higher temperatures than alkanes of similar molecular weight, but lower than alcohols of similar molecular weight because they cannot form hydrogen bonds with each other.

Reason for higher boiling point than alkanes (Aldehydes/Ketones)

They have permanent dipole-dipole moments (O = electronegative and C = electropositive) and the carbonyl group has greater mass/surface area increasing London dispersion forces.

Water Solubility of Aldehydes and Ketones

Soluble in common organic solvents; those with fewer than 5-6 carbon atoms are water soluble due to hydrogen bonding with water molecules.

Hydrogen Bonding with Water (Aldehydes/Ketones)

Aldehydes and ketones can form hydrogen bonds with water molecules.

Odors and Toxicity of Aldehydes and Ketones

Aldehydes and ketones have distinctive odors; ketones are generally less toxic than aldehydes.

Formaldehyde (HCHO)

At room temperature, it is a colorless gas with a pungent and suffocating odor; toxic, causes irritation, kidney damage, coma, and death; a breakdown product of methyl alcohol.

Formalin

A 37% aqueous solution of formaldehyde, used for disinfecting and sterilizing equipment by reacting with amino groups present in proteins.

Paraformaldehyde

A solid formed by the polymerization of formaldehyde on standing.

Acetaldehyde (CH3CHO)

A sweet-smelling, flammable liquid formed by the oxidation of ethyl alcohol; less toxic than formaldehyde, a general narcotic in large doses, used for the preparation of polymeric resins and silvering of mirrors.

Acetone (CH3COCH3)

One of the most widely used organic solvents, dissolving most organic compounds and water; volatile and a serious fire and explosion hazard; accumulates during excessive degradation of fats (fasting).

Benzaldehyde

A colorless liquid with a pleasant almond or cherry-like odor; used as a flavoring and fragrance in food, cosmetics, pharmaceuticals, and soap; serves as a forerunner to other organic molecules.

Oxidation of Aldehydes

Aldehydes can be oxidized to carboxylic acids by replacing the hydrogen on the carbonyl carbon with an –OH group.

Oxidation of Ketones

Ketones cannot be easily oxidized to carboxylic acids because they lack the hydrogen atom on the carbonyl carbon.

Reduction of Aldehydes and Ketones

Aldehydes and ketones can be reduced to alcohols (the opposite direction of oxidation).

Mechanism of Carbonyl Reduction

Occurs with the addition of hydrogen (H2) across the double bond to produce a hydroxyl group (-OH).

Products of Aldehyde Reduction

Aldehydes are reduced to primary alcohols.

Products of Ketone Reduction

Ketones are reduced to secondary alcohols.

Hydride anion (:H-) in Reduction

In reduction, a hydride anion (:H-) donates a lone pair of valence electrons to form a covalent bond with the carbonyl carbon.

NADH (Nicotinamide Adenine Dinucleotide)

A coenzyme that facilitates the reduction of carbonyl groups in biological systems.

Addition Reactions of Aldehydes and Ketones

Aldehydes and ketones undergo reactions in which an alcohol combines with the carbonyl carbon and oxygen.

Hemiacetal

The initial product of addition reactions between an alcohol and an aldehyde or ketone, having both an alcohol-like group (–OH) and an ether-like group (–OR) bonded to what was once the carbonyl carbon atom.

Hemiacetal Formation (Mechanism)

The H from the alcohol bonds to the carbonyl oxygen, and the OR from the alcohol bonds to the carbonyl carbon.

Stability of Hemiacetals

Hemiacetals may rapidly revert back to aldehydes or ketones by loss of alcohol, establishing an equilibrium; they are often too unstable to be isolated unless the –OH and CHO functional groups react within the same molecule (cyclic hemiacetals).

Acetal Formation

Formed from an alcohol and an aldehyde (via a hemiacetal intermediate) with an acid catalyst; a compound that has two ether-like groups (R-O-R) bonded to what was once the carbonyl carbon.

Acetal vs. Ketal

An acetal is formed from an aldehyde and an alcohol, while a ketal is formed from a ketone and an alcohol.

Hemiketal

A compound with a carbon atom bonded to two oxygen atoms, with one being an –OH group and one an –OR group, where the other two groups bonded to that carbon are carbons (derived from a ketone).

Hydrolysis

A reaction in which a bond is broken and the H– and –OH of water add to the atoms of the broken bond.

Acetal Hydrolysis

The reversal of acetal formation, which requires an acid catalyst and a large quantity of water to drive the reaction back toward the aldehyde or ketone and alcohol.